Method for integrally molding metal and resin and metal-resin composite structure obtainable by the same

ABSTRACT

A method for integrally molding a metal and a resin and a metal-resin composite structure obtainable by the same are provided. The method comprises forming a nanopore in a surface of a metal sheet; melting a thermoplastic resin on the surface of the metal sheet formed with the nanopore; and injection molding the thermoplastic resin onto the surface of the metal sheet. The thermoplastic resin includes a mixture of a main resin and a polyolefin resin, the main resin is a polycarbonate, and the polyolefin resin has a melting point of about 65° C. to about 105° C.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of International Patent ApplicationNo. PCT/CN2012/078832, filed on Jul. 18, 2012, which claims priority toand benefits of Chinese Patent Application Serial No. 201210043644.X,filed with the State Intellectual Property Office of P.R. China on Feb.24, 2012. The entire content of the above-referenced applications isincorporated herein by reference.

FIELD

The present disclosure relates to the field of metal-plastic molding,and more particularly to a method for integrally molding a metal and aresin, and a metal-resin composite structure obtained by the same.

BACKGROUND

In the fields of manufacture of articles such as automobiles, householdappliances and industrial machines, a metal and a resin often need to befirmly bonded together. Currently, in a conventional method, an adhesiveis used at normal temperature or under heating to integrally bond ametal and a synthetic resin. Alternatively, an engineering resin withhigh strength may also be bonded to a magnesium alloy, an aluminumalloy, or ferroalloys such as stainless steel directly without anadhesive.

Nano molding technology (NMT) is a technique of integrally bonding ametal and a resin, which allows the resin to be directly injectionmolded on a surface of a metal sheet by nano molding the surface of themetal sheet so as to obtain a metal-resin integrally molded product. Foreffective bonding of a metal and a resin, NMT may replace commonly usedinsert molding or zinc-aluminum or magnesium-aluminum die casting so asto provide a metal-resin integrally molded product with low cost andhigh performance. Compared with the bonding technology, NMT may reducethe weight of the product, ensure excellent strength of the mechanicalstructure, high processing rate, and high output, allow more appearancedecoration methods, applicable to vehicles, IT equipment, and 3Cproducts.

Japan's Taisei Plas Co., Ltd. filed a series of patent applicationsincluding, for example, CN1492804A, CN1717323A, CN101341023A andCN101631671A, which disclose methods for integrally molding a metal anda resin composition. For example, by using a resin compositioncontaining polyphenylene sulfide (PPS), polybutylene terephthalate(PBT), and polyamide (PA) with high crystallinity as an injectionmolding material, the resin composition is directly injection molded ona surface of a nano molded aluminum alloy layer to allow the resincomposition to immerse in a nanoscale micropore, so as to obtain ametal-resin integrally molded product with a certain mechanicalstrength. However, because the resins used in these methods are allhighly crystalline resins, the resins cannot be made into componentswith transparency, thereby restricting the design and application of theproduct.

SUMMARY

Embodiments of the present disclosure seek to solve at least one of theproblems existing in the prior art to at least some extent, particularlytechnical problems of complex molding process, unduly restrictiveconditions, the difficulty in processing the surface of the plasticlayer, the difficulty in applying to the surface decoration of a plasticarticle, and low mechanical strength when the plastic is a highlycrystalline resin in nano molding technology (NMT).

According to a first aspect of the present disclosure, there is provideda method for integrally molding a metal and a resin. The methodcomprises steps of:

-   A) forming a nanopore in a surface of a metal sheet; and-   B) melting a thermoplastic resin on the surface of the metal sheet    formed with the nanopore, and then injection molding the    thermoplastic resin onto the surface of the metal sheet,-   in which the thermoplastic resin is a mixture of a main resin and a    polyolefin resin, the main resin is a polycarbonate, and the    polyolefin resin has a melting point of about 65° C. to about 105°    C.

According to a second aspect of the present disclosure, there isprovided a metal-resin composite structure, which may be obtained by themethod according to the first aspect of the present disclosure.

In the method for integrally molding the metal and the resin accordingto an embodiment of the present disclosure, a polycarbonate with higherlight transmittance is used, and a polyolefin resin with a melting pointof about 65° C. to about 105° C. is also used. Therefore, injectionmolding at a specific mould temperature may not be required during themolding, subsequent annealing treatment may also not be required, themolding process may be simplified, and it may be ensured that theobtained metal-resin composite structure may have high mechanicalstrength and good surface treatment characteristics, thus enhancing thelight transmittance of a plastic article.

Additional aspects and advantages of embodiments of present disclosurewill be given in part in the following descriptions, become apparent inpart from the following descriptions, or be learned from the practice ofthe embodiments of the present disclosure.

DETAILED DESCRIPTION

Reference will be made in detail to embodiments of the presentdisclosure. The embodiments described herein are explanatory,illustrative, and used to generally understand the present disclosure.The embodiments shall not be construed to limit the present disclosure.

According to a first aspect of the present disclosure, a method forintegrally molding a metal and a resin is provided. The method comprisessteps of:

-   A) forming a nanopore in a surface of a metal sheet; and-   B) melting a thermoplastic resin on the surface of the metal sheet    formed with the nanopore, and then injection molding the    thermoplastic resin onto the surface of the metal sheet, in which    the thermoplastic resin is a mixture of a main resin and a    polyolefin resin, the main resin is a polycarbonate, and the    polyolefin resin has a melting point of about 65° C. to about 105°    C.

Because the resins used in the prior art are all highly crystallineresins, the surface of the prior art plastic layer may be difficult totreat. In the present disclosure, a non-crystalline polycarbonate, whichhas a surface gloss and a toughness both superior to those of the highlycrystalline resins in the prior art, is used as an injection moldingmaterial, and a polyolefin resin with a melting point of about 65° C. toabout 105° C. is also used. Therefore, injection molding at a specificmould temperature may not be required during the molding. Subsequentannealing treatment may also not be required. The molding process may besimplified. And it may be ensured that the obtained metal-resincomposite structure has high mechanical strength and good surfacetreatment characteristics, thus solving the problem of the conventionaltechniques and enhancing the light transmittance of plastic articles.

In the present disclosure, the mechanism of the metal-resin integrallymolding is as follows: a nanoscale micropore is formed on the surface ofthe metal sheet; a resin composition is melted on the surface of themetal sheet, where a part of the melted resin composition permeates intothe nanoscale micropore; and then the metal and the resin compositionare integrally injection molded.

Particularly, in step A), forming a nanopore on a surface of a metalsheet comprises: anodizing the surface of the metal sheet to form anoxide layer on the surface of the metal sheet, in which the oxide layeris formed with the nanopore. The anodizing technique is well known tothose skilled in the art. In some embodiments, anodizing the surface ofthe metal sheet may comprise: placing a pretreated metal sheet as ananode in a H₂SO₄ solution with a concentration of about 10 wt % to about30 wt %; and electrolyzing the metal at a temperature of about 10° C. toabout 30° C. at a voltage of about 10V to about 100V for about 1 min toabout 40 min to form the oxide layer with a thickness of about 1 μm toabout 10 μm on the surface of the metal sheet. An anodizing apparatusmay be those known in the art, such as, an anodizing bath.

By anodizing, the oxide layer formed with the nanopore is formed on thesurface of the metal sheet. Preferably, the oxide layer has a thicknessof about 1 μm to about 10 μm, more preferably about 1 μm to about 5 μm.

According to an embodiment, the nanopore has a diameter of about 10 nmto about 100 nm. According to a further embodiment, the nanopore has adiameter of about 20 nm to about 80 nm. According to a still furtherembodiment, the nanopore has a diameter of about 20 nm to about 60 nm.According to an embodiment, the nanopore has a depth of about 0.5 μm toabout 9.5 μm. According to a further embodiment, the nanopore has adepth of about 0.5 μm to about 5 μm. The structure of the nanoporeenhances the filling of the melted resin composition in the nanopore.The nanopore with such depth may be filled with the melted resin in aconventional injection molding process, which, while retaining thebonded area between the resin and the oxide layer, may further improvethe bonding force between the resin and the metal because there are novoids or gaps in the nanopore.

In one preferred embodiment, in step A), forming a nanopore in a surfaceof a metal sheet may further comprise a step of: immersing the metalsheet formed with the oxide layer on the surface thereof in an etchingsolution to form a corrosion pore in an outer surface of the oxidelayer. The corrosion pore is communicated with the nanopore. Thecorrosion pore and the nanopore form a double-layer three-dimensionalpore structure, thereby enhancing the permeability of the resincomposition, improving the bonding force between the resin compositionand the metal, and thus further facilitating the molding.

According to an embodiment, the corrosion pore has a diameter of about200 nm to about 2000 nm. According to a further embodiment, thecorrosion pore has a diameter of about 200 nm to about 1000 nm.According to a still further embodiment, the corrosion pore has adiameter of about 400 nm to about 1000 nm. According to an embodiment,the corrosion pore has a depth of about 0.5 μm to about 9.5 μm.According to a further embodiment, the corrosion pore has a depth ofabout 0.5 μm to about 5 μm. The structure of the corrosion porefacilitates direct injection of the resin composition and the bondingbetween the resin composition and the alloy during the injectionmolding.

The etching solution may be a solution that corrodes the oxide layer.Generally, the etching solution may be a solution that dissolves theoxide layer. The concentration of the etching solution may be adjustedas desired. The etching solution may be an acid/base etching solution.Preferably, the etching solution may be a single basic solution with apH of about 10 to about 13 or a complex buffer solution. The singlebasic solution with a pH of about 10 to about 13 may be at least oneselected from the group consisting of a Na₂CO₃ aqueous solution, aNaHCO₃ aqueous solution, and a NaOH aqueous solution, preferably aNa₂CO₃ aqueous solution and/or a NaHCO₃ aqueous solution, thus allowingthe corrosion pores to be uniformly distributed in the surface of theoxide layer and to have uniform diameter, and achieving better bondingperformance between the resin layer and an aluminum alloy substrate aswell as higher tensile strength and better integral bonding of analuminum alloy composite structure. The Na₂CO₃ aqueous solution and/orthe NaHCO₃ aqueous solution may have a solid content of about 0.1 wt %to about 15 wt %. The complex buffer solution may be a mixed solution ofa soluble hydrophosphate and a soluble base, for example, an aqueoussolution of sodium dihydrogen phosphate and sodium hydroxide. Theaqueous solution of sodium dihydrogen phosphate and sodium hydroxide mayhave a solid content of about 0.1 wt % to about 15 wt %.

Immersing the metal sheet formed with the oxide layer on the surfacethereof in an etching solution may comprise repeatedly immersing themetal sheet in the etching solution 2 to 10 times with each immersingtime of about 1 minute to 60 minutes, and cleaning the metal sheet withdeionized water after each immersing. Cleaning the metal sheet maycomprise placing the metal sheet in a washing bath to wash the metalsheet for about 1 minute to about 5 minutes, or placing the metal sheetin a washing bath to place the metal sheet for about 1 min to about 5minutes.

It has been found by the inventors through many experiments that in thepresent disclosure, by using a polyolefin resin with a melting point ofabout 65° C. to about 105° C. in the non-crystalline main resin, theflowing capability of the resin in the nano on the surface of the metalsheet may be enhanced, thus ensuring strong adhesive force between themetal and the plastic as well as high mechanical strength of themetal-resin composite structure. Preferably, based on 100 weight partsof the thermoplastic resin, the amount of the main resin is about 95weight parts to about 99 weight parts, and the amount of the polyolefinresin is about 1 weight part to about 5 weight parts.

It has also been found by the inventors that by using a flow improver inthe thermoplastic resin, the flowing capability of the resin may beenhanced, thus further enhancing the adhesive force between the metaland the plastic as well as the injection molding performance of theresin. Preferably, based on 100 weight parts of the thermoplastic resin,the thermoplastic resin further contains about 1 weight part to about 5weight parts of a flow improver. Preferably, the flow improver is amethyl methacrylate composition.

In the present disclosure, the main resin is a polycarbonate (PC), whichmay be selected from any straight chain polycarbonate and/or anybranched chain polycarbonate commonly used in the prior art. Forexample, the polycarbonate may be PC IR2500 or IR2200 available fromIdemitsu Kosan Co., Ltd., without special limits.

In the present disclosure, the polyolefin resin has a melting point ofabout 65° C. to about 105° C. Preferably, the polyolefin resin may be agrafted polyethylene. More preferably, the polyolefin resin may be agrafted polyethylene with melting point of about 100° C. or about 105°C.

In the present disclosure, the metal may be any metal known, and may beselected according to the specific application. For example, the metalmay be at least one selected from the group consisting of aluminum,stainless steel and magnesium.

According to a second aspect of the present disclosure, a metal-resincomposite structure is also provided, which is obtained by the methodaccording to the first aspect of the present disclosure.

In the metal-resin composite structure according to an embodiment of thepresent disclosure, the metal sheet and the plastic layer are integrallyformed, providing strong adhesive force and high mechanical strength. Asshown in Table 1, each metal-resin composite structure has a fracturestrength of about 15 MPa to about 20 MPa, an impact strength of about350 J/m to about 400 J/m and a light transmittance of about 50% to about52%.

The present disclosure provides further details of the embodiments withreference to examples thereof. It would be appreciated that particularexamples described herein are merely used to understand the presentdisclosure. The examples shall not be construed to limit the presentdisclosure. The raw materials used in the examples and the comparativeexamples are all commercially available, without special limits.

EXAMPLE 1 Pretreatment

A commercially available A5052 aluminum alloy plate with a thickness of1 mm was cut into 18 mm×45 mm rectangular sheets, which were thenimmersed in a 40 g/L NaOH aqueous solution. The temperature of the NaOHaqueous solution was 40° C. After 1 minute, the rectangular sheets werewashed with water and dried to obtain pretreated aluminum alloy sheets.

(2) Surface Treatment 1:

Each aluminum alloy sheet as an anode was placed in an anodizing bathcontaining a 20 wt % H₂SO₄ solution, the aluminum alloy was electrolyzedat a voltage of 20V at 18° C. for 10 min, and then the aluminum alloysheet was blow-dried.

The cross section of the aluminum alloy sheet after the surfacetreatment 1 was observed by a metalloscope, to find out that an aluminumoxide layer with a thickness of 5 μm was formed on the surface of theelectrolyzed aluminum alloy sheet. The surface of the aluminum alloysheet after the surface treatment 1 was observed by an electronmicroscope, to find out that a nanopore with a diameter of about 40 nmto about 60 nm and a depth of 1 μm was formed in the aluminum oxidelayer.

(3) Surface Treatment 2:

500 ml of 10 wt % sodium carbonate solution (pH=12) with a temperatureof 20° C. was prepared in a beaker. The aluminum alloy sheet after step(2) was immersed in the sodium carbonate solution, taken out after 5minutes, and placed in a beaker containing water to be immersed for 1minute. The process was repeated for 5 times. After water immersing forthe last time, the aluminum alloy sheet was blow-dried.

The surface of the aluminum alloy sheet after the surface treatment 2was observed by an electron microscope, to find out that a corrosionpore with a diameter of 300 nm to 1000 nm and a depth of 4 μm was formedin the surface of the immersed aluminum alloy sheet. It may also beobserved that there was a double-layer three-dimensional pore structurein the aluminum oxide layer, and the corrosion pore was communicatedwith the nanopore.

(4) Molding:

95 weight parts of a straight chain polycarbonate PC (IR2200 availablefrom Idemitsu Kosan Co., Ltd.), 3 weight parts of a flow improver (TP003available from Mitsubishi Rayon Co., Ltd.) and 2 weight parts of agrafted polyethylene with a melting point of 65° C. (Lotader AX8900available from Arkema Group) were weighed, and mixed uniformly to obtaina resin mixture. Then, using an injection molding machine, the meltedresin mixture was injection molded on the surface of the aluminum alloysheet after step (3), to obtain a metal-resin composite structure S1 inthis example.

EXAMPLE 2

A metal-resin composite structure S2 in this example was prepared by amethod which is substantially the same as the method in Example 1, withthe following exceptions.

In step (1), instead of the aluminum alloy plate in Example 1, acommercially available magnesium alloy plate with a thickness of 3 mmwas cut into 18 mm×45 mm rectangular sheets.

In step (2), each magnesium alloy sheet as an anode was placed in ananodizing bath containing a 20 wt % H₂SO₄ solution. The magnesium alloywas electrolyzed at a voltage of 15V at 18° C. for 10 min. And then themagnesium alloy sheet was blow-dried.

The cross section of the magnesium alloy sheet after the surfacetreatment 1 was observed by a metalloscope, to find out that a magnesiumoxide layer with a thickness of 5 μm was formed on the surface of theelectrolyzed magnesium alloy sheet. The surface of the magnesium alloysheet after the surface treatment 1 was observed by an electronmicroscope, to find out that a nano micropore with a diameter of 20 nmto 40 nm and a depth of 1 μm was formed in the magnesium oxide layer.

The surface of the magnesium alloy sheet after the surface treatment 2was observed by an electron microscope, to find out that a corrosionpore with a diameter of 300 nm to 1000 nm and a depth of 4 μm was formedin the surface of the immersed magnesium alloy sheet. It may also beobserved that there was a double-layer three-dimensional pore structurein the magnesium oxide layer, and the corrosion pore was communicatedwith the nanopore.

After the above steps, the metal-resin composite structure S2 in thisexample was obtained.

EXAMPLE 3

A metal-resin composite structure S3 in this example was prepared by amethod which is substantially the same as the method in Example 1, withthe following exceptions.

In step (2), each aluminum alloy sheet as an anode was placed in ananodizing bath containing a 20 wt % H₂SO₄ solution, the aluminum alloywas electrolyzed at a voltage of 40V at 18° C. for 10 min, and then thealuminum alloy sheet was blow-dried.

The cross section of the aluminum alloy sheet after the surfacetreatment 1 was observed by a metalloscope, to find out that an aluminumoxide layer with a thickness of 5 μm was formed on the surface of theelectrolyzed aluminum alloy sheet. The surface of the aluminum alloysheet after the surface treatment 1 was observed by an electronmicroscope, to find out that a nanopore with a diameter of 60 nm to 80nm and a depth of 1 μm was formed in the aluminum oxide layer.

The surface of the aluminum alloy sheet after the surface treatment 2was observed by an electron microscope, to find out that a corrosionpore with a diameter of 300 nm to 1000 nm and a depth of 4 μm was formedin the surface of the immersed aluminum alloy sheet. It may also beobserved that there was a double-layer three-dimensional pore structurein the aluminum oxide layer, and the corrosion pore was communicatedwith the nanopore.

After the above steps, the metal-resin composite structure S3 in thisexample was obtained.

EXAMPLE 4

A metal-resin composite structure S4 in this example was prepared by amethod which is substantially the same as the method in Example 2, withthe following exceptions.

In step (4), 98 weight parts of a straight chain polycarbonate PC(IR2200 available from Idemitsu Kosan Co., Ltd.) and 2 weight parts of agrafted polyethylene with a melting point of 105° C. (Lotader 4210available from Arkema Group) were weighed, and mixed uniformly to obtaina resin mixture. Then, using an injection molding machine, the meltedresin mixture was injection molded on the surface of the aluminum alloysheet after step (3), to obtain a metal-resin composite structure S4 inthis example.

COMPARATIVE EXAMPLE 1

A metal-resin composite structure DS1 in this example was prepared by amethod which is substantially the same as the method in Example 1, withthe following exceptions.

In step (4), 97 weight parts of a straight chain polycarbonate PC(IR2200 available from Idemitsu Kosan Co., Ltd.) and 3 weight parts of aflow improver (TP003 available from Mitsubishi Rayon Co., Ltd.) wereweighed, and mixed uniformly to obtain a resin mixture. Then, using aninjection molding machine, the melted resin mixture was injection moldedon the surface of the aluminum alloy sheet after step (3), to obtain ametal-resin composite structure DS1 in this example.

COMPARATIVE EXAMPLE 2

A metal-resin composite structure DS2 in this example was prepared by amethod which is substantially the same as the method in Example 1, withthe following exceptions.

In step (4), 84 weight parts of polyphenylene sulfide PPS (PPS-HClavailable from Sichuan Deyang Chemical Co., Ltd., China), 3 weight partsof a flow improver, i.e., a cyclic polyester (CBT100), 8 weight parts ofa grafted polyethylene with a melting point of 105° C. (Lotader AX8900available from Arkema Group) and 5 weight parts of a toughener (LotaderAX8840 available from Arkema Group) were weighed, and mixed uniformly toobtain a resin mixture. Then, using an injection molding machine, themelted resin mixture was injection molded on the surface of the aluminumalloy sheet after step (3) to obtain an injection molded metal-resincomposite structure, which was annealed at 180° C. for 1 hour to obtaina metal-resin composite structure DS2 in this example.

Performance Test

1) The metal-resin composite structures S1-S4 and DS1-DS4 were fixed ona universal testing machine for tensile test to obtain maximum loadsthereof respectively. The test results were shown in Table 1.

2) The impact strength of standard samples of the metal-resin compositestructures S1-S4 and DS1-DS4 was tested using a cantilever beam impacttester according to the method disclosed in ASTM D256.

3) 40.0 mm×40.0 mm×2.0 mm square samples were made of the resin mixturesin Examples 1-4 and Comparative Examples 1-2 respectively, and the lighttransmittance of the square samples were tested using aspectrophotometer respectively.

The test results were shown in Table 1.

TABLE 1 Fracture Impact Light Fracture Impact Light Strength StrengthTransmittance Strength Strength Transmittance Sample (MPa) (J/m) (%)Sample (MPa) (J/m) (%) S1 22 350 50 S2 20 350 50 S3 19 350 50 S4 19 40052 DS1 10 500 55 DS2 20 130 —

It may be seen from the test results in Table 1 that the metal-resincomposite structures S1-S4 have a fracture strength of about 19 MPa toabout 22 MPa, which indicates that the bonding force between the metalsheet and the plastic layer in the metal-resin composite structuresS1-S4 is very strong; the metal-resin composite structures S1-S4 have animpact strength of about 350 J/m to about 400 J/m, which indicates thatthe metal-resin composite structures S1-S4 have high mechanicalstrength; and the metal-resin composite structures S1-S4 have a lighttransmittance of about 50% to about 52%, which may meet the requirementof light transmission applications.

By comparing the test results of the metal-resin composite structure S1with the test results of the metal-resin composite structure DS2, it maybe seen that the toughness of the polyphenylene oxide resin used in theprior art is very poor, the toughness of the polyphenylene oxide resinafter modified with a toughener is still poor, and the metal-resincomposite structure DS2 is unable to meet the requirement of the lighttransmission applications.

Although explanatory embodiments have been shown and described, it wouldbe appreciated by those skilled in the art that the above embodimentscan not be construed to limit the present disclosure, and changes,alternatives, and modifications can be made in the embodiments withoutdeparting from spirit, principles and scope of the present disclosure.

What is claimed is:
 1. A method for integrally molding a metal and aresin, comprising: forming a nanopore on a surface of a metal sheet;melting a thermoplastic resin on the surface of the metal sheetincluding the nanopore; and injection molding the melted thermoplasticresin onto the surface of the metal sheet, wherein the thermoplasticresin includes a mixture of a main resin and a polyolefin resin, themain resin is a polycarbonate, and the polyolefin resin has a meltingpoint of about 65° C. to about 105° C.
 2. The method according to claim1, wherein forming the nanopore on the surface of the metal sheetcomprises: anodizing the surface of the metal sheet to form an oxidelayer on the surface of the metal sheet, where the oxide layer includesthe nanopore.
 3. The method according to claim 2, wherein the oxidelayer has a thickness of about 1 μm to about 10 μm, and the nanopore hasa diameter of about 10 nm to about 100 nm and a depth of about 0.5 μm toabout 9.5 μm.
 4. The method according to claim 2, wherein anodizing thesurface of the metal sheet comprises: placing a pretreated metal sheetas an anode in a H₂SO₄ solution with a concentration of about 10 wt % toabout 30 wt %; and electrolyzing the metal sheet at a temperature ofabout 10° C. to about 30° C. at a voltage of about 10V to about 100V forabout 1 minute to about 40 minutes to form the oxide layer with athickness of about 1 μm to about 10 μm on the surface of the metalsheet.
 5. The method according to claim 2, wherein forming the nanoporeon the surface of the metal sheet further comprises: immersing the metalsheet including the oxide layer on the surface thereof in an etchingsolution to form a corrosion pore on an outer surface of the oxidelayer.
 6. The method according to claim 5, wherein the corrosion pore iscommunicated with the nanopore, and the corrosion pore has a diameter ofabout 200 nm to about 2000 nm and a depth of about 0.5 μm to about 9.5μm.
 7. The method according to claim 5, wherein the etching solutioncorrodes the oxide layer.
 8. The method according to claim 1, whereinbased on 100 weight parts of the thermoplastic resin, the amount of themain resin is about 95 weight parts to about 99 weight parts, and theamount of the polyolefin resin is about 1 weight part to about 5 weightparts.
 9. The method according to claim 8, wherein based on 100 weightparts of the thermoplastic resin, the thermoplastic resin furthercontains about 1 weight part to about 5 weight parts of a flow improver,and the flow improver is a cyclic polyester.
 10. The method according toclaim 1, wherein the polyolefin resin is a grafted polyethylene.
 11. Themethod according to claim 1, wherein the metal is at least one selectedfrom the group consisting of aluminum, stainless steel and magnesium.12. A metal-resin composite structure, comprising: a metal sheetincluding a nanopore formed on a surface thereof; a thermoplastic resininjection molded onto the surface of the metal sheet, wherein thethermoplastic resin includes a mixture of a main resin and a polyolefinresin, the main resin is a polycarbonate, and the polyolefin resin has amelting point of about 65° C. to about 105° C.
 13. The metal-resincomposite structure of claim 12, wherein the metal sheet furtherincludes an oxide layer formed by anodizing the surface of the metalsheet, and wherein the oxide layer includes the nanopore.
 14. Themetal-resin composite structure of claim 13, wherein the oxide layer hasa thickness of about 1 μm to about 10 μm, and the nanopore has adiameter of about 10 nm to about 100 nm and a depth of about 0.5 μm toabout 9.5 μm.
 15. The metal-resin composite structure of claim 13,wherein the metal sheet is a pretreated metal sheet, and the oxide layeris formed by placing the pretreated metal sheet as an anode in a H₂SO₄solution with a concentration of about 10 wt % to about 30 wt % andelectrolyzing the metal sheet at a temperature of about 10° C. to about30° C. at a voltage of about 10V to about 100V for about 1 minute toabout 40 minutes.
 16. The metal-resin composite structure of claim 13,wherein the oxide layer includes a corrosion pore on an outer surface ofthe oxide layer.
 17. The metal-resin composite structure of claim 16,wherein the corrosion pore is communicated with the nanopore, and thecorrosion pore has a diameter of about 200 nm to about 2000 nm and adepth of about 0.5 μm to about 9.5 μm.
 18. The metal-resin compositestructure according to claim 12, wherein based on 100 weight parts ofthe thermoplastic resin, the amount of the main resin is about 95 weightparts to about 99 weight parts, and the amount of the polyolefin resinis about 1 weight part to about 5 weight parts.
 19. The metal-resincomposite structure according to claim 18, wherein based on 100 weightparts of the thermoplastic resin, the thermoplastic resin furthercontains about 1 weight part to about 5 weight parts of a flow improver,and the flow improver is a cyclic polyester.
 20. The metal-resincomposite structure according to claim 12, wherein the polyolefin resinis a grafted polyethylene and the metal is at least one selected fromthe group consisting of aluminum, stainless steel and magnesium.